Multilayer capacitor

ABSTRACT

A multilayer capacitor includes a body including a stacked structure having dielectric layers, and internal electrodes, and external electrodes. The body has a central portion, and cover portions disposed above and below the central portion, the body has a first surface and a second surface to which the internal electrodes are exposed and which oppose each other, a third surface and a fourth surface which oppose each other in the stacking direction of the dielectric layers, and a fifth surface and a sixth surface which are connected to the first to fourth surfaces and oppose each other, and a surface roughness of each of the third to sixth surfaces of the body is greater than a surface roughness of each of the first and second surfaces of the body.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims benefit of priority to Korean Patent ApplicationNo. 10-2018-0138076 filed on Nov. 12, 2018 in the Korean IntellectualProperty Office, the disclosure of which is incorporated herein byreference in its entirety.

TECHNICAL FIELD

The present disclosure relates to a multilayer capacitor.

BACKGROUND

A capacitor is an element that may store electricity therein, and when avoltage is applied to the capacitor in a state in which two electrodesare disposed to face each other, electricity is accumulated in therespective electrodes. When a direct current (DC) voltage is applied tothe capacitor, current flows in the capacitor while an electrical chargeis accumulated, but when the accumulation of the electricity iscompleted, the current does not flow in the capacitor. Meanwhile, whenan alternating current (AC) voltage is applied to the capacitor, an ACcurrent flows in the capacitor while polarities of the electrodes arealternated.

Such a capacitor may be divided into several types of capacitor such asan aluminum electrolytic capacitor, in which electrodes are formed ofaluminum and a thin oxide layer is disposed between the electrodesformed of aluminum, a tantalum capacitor, in which tantalum is used asan electrode material, a ceramic capacitor, in which a dielectricmaterial having a high dielectric constant, such as a barium titanate,is used between electrodes, a multilayer ceramic capacitor (MLCC), inwhich a ceramic having a high dielectric constant is used in amultilayer structure as a dielectric material provided betweenelectrodes, a film capacitor in which a polystyrene film is used as adielectric material provided between electrodes, and the like, dependingon a kind of insulator provided between electrodes.

Thereamong, the multilayer ceramic capacitor has recently mainly beenused in various fields such as a high frequency circuit, and the like,since it has excellent temperature characteristics and frequencycharacteristics and may be implemented to have a small size.

A multilayer ceramic capacitor according to the related art includes alaminate formed by stacking a plurality of dielectric sheets andexternal electrodes formed on external surfaces of the laminate andhaving different polarities, wherein internal electrodes alternatelystacked in the laminate may be electrically connected to the respectiveexternal electrodes.

Recently, in accordance with miniaturization and an increase in a degreeof integration of an electronic product, many studies of miniaturizationand an increase in a degree of integration of the multilayer ceramiccapacitor have been conducted. Particularly, in the multilayer ceramiccapacitor, various attempts at increasing the number of stackeddielectric layers and improving the connectivity of internal electrodesby decreasing thicknesses of the dielectric layers in order to increasea capacitance of the multilayer ceramic capacitor and miniaturize themultilayer ceramic capacitor have been conducted.

Particularly, in developing a multilayer ceramic capacitor havingultrahigh capacitance, it has become more important to securereliability of a product in which the numbers of stacked thin filmdielectric layers and internal electrodes are high. As the numbers ofstacked dielectric layers and internal electrodes are increased, stepsdue to thickness differences between the internal electrodes and thedielectric layers are increased. These steps cause a warpage phenomenonin distal end portions of the internal electrodes due to stretching ofthe dielectric layers in a transversal direction in a densifying processof compressing a body.

For example, the distal end portions of the internal electrodes are bentin order to fill the steps, and in margin portions, empty spaces due tothe steps are removed by depression of covers and a reduction in amargin width. The empty spaces due to the steps are removed, such thatcapacitance layers are also stretched by the reduced margin width.Reliability of the multilayer ceramic capacitor such as withstandvoltage characteristics or the like may be reduced due to structurallyirregular stretching of the internal electrodes as described above.

In order to solve such a problem, a method of cutting opposite endsurfaces of the body in a length direction and then attaching endsurface margin portions to the opposite end surfaces has been developed.However, such a method may be complicated, such that productivity may below, and when the end surface margin portions are formed to have a smallthickness, a thickness of corner margin portions also becomes small,such that moisture resistance reliability of the body is deteriorated.

SUMMARY

An aspect of the present disclosure is to provide a multilayer capacitorin which an effective volume may be significantly increased and moistureresistance reliability may be secured.

According to an aspect of the present disclosure, a multilayer capacitorincludes a body including a stacked structure having a plurality ofdielectric layers, and a plurality of internal electrodes stacked withthe plurality of dielectric layers interposed therebetween, and externalelectrodes disposed on external surfaces of the body and electricallyconnected to the plurality of internal electrodes. The body has acentral portion, and cover portions disposed above and below the centralportion in a stacking direction of the plurality of dielectric layers,the body has a first surface and a second surface from which theplurality of internal electrodes are exposed and which oppose eachother, a third surface and a fourth surface which oppose each other inthe stacking direction of the plurality of dielectric layers, and afifth surface and a sixth surface which are connected to the first tofourth surfaces and oppose each other, and a surface roughness of eachof the third to sixth surfaces of the body is greater than a surfaceroughness of each of the first and second surfaces of the body.

In an aspect of the present disclosure, the surface roughness, Ra, ofeach of the third to sixth surfaces may satisfy the followingrelationship, based on an average calculation method: 0.2<Ra<0.6.

In an aspect of the present disclosure, the surface roughness, Rt, ofeach of the third to sixth surfaces may satisfy the followingrelationship, based on a maximum height calculation method: 2.0<Rt<5.0.

In an aspect of the present disclosure, the surface roughness, Rz, ofeach of the third to sixth surfaces may satisfy the followingrelationship, based on a ten-point average calculation method:2.0<Rz<5.0.

In an aspect of the present disclosure, corners of the cover portions inthe body may be formed as curved surfaces.

In an aspect of the present disclosure, a radius R of curvature of eachof the curved corners and a thickness T of the body may satisfy thefollowing relationship: 10 μm≤R≤T/4.

In an aspect of the present disclosure, a margin Wg of each of the fifthand sixth surfaces from each of the fifth and sixth surfaces to aninternal electrode closest to the surface of the body among theplurality of internal electrodes, and a margin Tg of each of the thirdand fourth surfaces from each of the third and fourth surfaces to aninternal electrode closest to the surface of the body among theplurality of internal electrodes, may satisfy the followingrelationship: 0.8≤Tg/Wg≤1.2.

In an aspect of the present disclosure, corners at which the thirdsurface is connected to the fifth and sixth surfaces, and corners atwhich the fourth surface is connected to the fifth and sixth surfaces,may have curved surfaces in the cover portions.

In an aspect of the present disclosure, a margin δ of each of thecorners having the curved surfaces in the cover portions may be greaterthan or equal to a margin Wg of each of the fifth and sixth surfaces.

In an aspect of the present disclosure, the margins (δ and Wg) maysatisfy the following relationship: 1≤δ/Wg≤1.2.

In an aspect of the present disclosure, the plurality of internalelectrodes may have a uniform width.

In an aspect of the present disclosure, in the plurality of internalelectrodes, a width of an internal electrode disposed in the coverportion may be narrower than a width of an internal electrode disposedin the central portion.

In an aspect of the present disclosure, a width of the internalelectrode disposed closer to the surface of the body, among theplurality of internal electrodes disposed in the cover portion, may benarrower.

In an aspect of the present disclosure, widths of the plurality ofinternal electrodes may be widths in a direction perpendicular to adirection connecting the first surface and the second surface, andwidths in a direction perpendicular to the stacking direction of theplurality of dielectric layers.

According to an aspect of the present disclosure, a multilayer capacitorincludes a body including: a stacked structure having dielectric layers,and first and second internal electrodes stacked with the dielectriclayers interposed therebetween and respectively exposed from endsurfaces of the body, and a margin covering the stacked structure exceptthe end surfaces; and first and second external electrodes disposed onthe end surfaces of the body and electrically connected to the first andsecond internal electrodes, respectively. A surface roughness of themargin is greater than a surface roughness of each of the end surfaces,and opposing ends of each of the first and second internal electrodes,in a width direction of the body, are in contact with the margin.

In an aspect of the present disclosure, the first and second internalelectrodes may include, central internal electrodes, upper internalelectrodes, and lower internal electrodes, the central internalelectrodes may be disposed between the upper internal electrodes and thelower internal electrodes, a difference between a largest width and asmallest width of the central internal electrodes may be less than 0.1μm, a width of the upper internal electrodes may decrease in a directionfrom the central internal electrodes to the upper internal electrodes,and a width of the lower internal electrodes may decrease in a directionfrom the central internal electrodes to the lower internal electrodes.

In an aspect of the present disclosure, a difference between a largestwidth and a smallest width of the internal electrodes may be less than0.1 μm, and a distance, in a stacking direction of the dielectriclayers, from an uppermost inner electrode of the first and secondinternal electrodes to an exterior upper surface of the margin, or adistance, in the stacking direction of the dielectric layers, from alowermost inner electrode of the first and second internal electrodes toan exterior lower surface of the margin, may be greater than a distance,in the width direction of the body, from each of the first and secondinternal electrodes to an exterior side surface of the margin.

In an aspect of the present disclosure, one of the following conditionsis satisfied: 0.2 μm<Ra<0.6 μm, in which Ra is the surface roughness ofmargin based on an average calculation method, 2.0 μm<Rt<5.0 μm, inwhich Rt is the surface roughness of margin based on a maximum heightcalculation method, and 2.0 μm<Rz<5.0 μm, in which Rz is the surfaceroughness of margin based on a ten-point average calculation method.

In an aspect of the present disclosure, the margin may include aplurality of layers each having pores.

In an aspect of the present disclosure, a thickness of a curved portionof the margin at a corner of the body may be equal to greater than athickness of a flat portion of the margin disposed on a side surface ofthe body in the width direction.

BRIEF DESCRIPTION OF DRAWINGS

The above and other aspects, features, and advantages of the presentdisclosure will be more clearly understood from the following detaileddescription, taken in conjunction with the accompanying drawings, inwhich:

FIG. 1 is a schematic perspective view illustrating an appearance of amultilayer capacitor according to an embodiment in the presentdisclosure;

FIG. 2 is a cross-sectional view taken along line I-I′ of the multilayercapacitor of FIG. 1;

FIG. 3 is a schematic view illustrating a surface roughness of the thirdto sixth surfaces among the bodies of the multilayer capacitor of FIG.1;

FIG. 4 is a cross-sectional view taken along line II-II′ of themultilayer capacitor of FIG. 1;

FIG. 5 is a schematic view illustrating a surface roughness of the firstand second surfaces among the bodies of the multilayer capacitor of FIG.1;

FIG. 6 is a cross-sectional view taken along line I-I′ of the multilayercapacitor of FIG. 1, in which edges of a region of internal electrodesare denoted by dotted lines;

FIGS. 7 and 8 are views illustrating shapes of a body and an internalelectrode that may be employed in a multilayer capacitor according toanother embodiment of the present disclosure; and

FIGS. 9 to 18 are views illustrating processes of manufacturing amultilayer capacitor according to an embodiment in the presentdisclosure.

DETAILED DESCRIPTION

Hereinafter, embodiments of the present disclosure will be described asfollows with reference to the attached drawings. However, embodiments ofthe present disclosure may be modified into various other forms, and thescope of the present disclosure is not limited to the embodimentsdescribed below. Embodiments of the present disclosure may be alsoprovided to more fully describe the present disclosure to those skilledin the art. Therefore, the shapes and sizes of the elements in thedrawings may be exaggerated for clarity, and the elements denoted by thesame reference numerals in the drawings are the same elements.

In order to clearly illustrate the present disclosure, parts not relatedto the description are omitted, and thicknesses are enlarged in order toclearly represent layers and regions, and similar portions are denotedby similar reference numerals throughout the specification. Throughoutthe specification, when an element is referred to as “comprising”, itmeans that it may include other elements as well, rather than excludingother elements unless specifically stated otherwise.

FIG. 1 is a schematic perspective view illustrating an appearance of amultilayer capacitor according to an embodiment in the presentdisclosure. FIGS. 2 and 6 are cross-sectional views taken along lineI-I′ of the multilayer capacitor of FIG. 1, and in FIG. 6, an outer sideof a region in which internal electrodes are disposed is denoted bydotted lines. FIG. 3 is a schematic view illustrating a surfaceroughness of the third to sixth surfaces among the bodies of themultilayer capacitor of FIG. 1. FIG. 4 is a cross-sectional view takenalong line II-II′ of the multilayer capacitor of FIG. 1. FIG. 5 is aschematic view illustrating a surface roughness of the first and secondsurfaces among the bodies of the multilayer capacitor of FIG. 1.

Referring to the drawings, a multilayer capacitor 100 according to anembodiment of the present disclosure may include a body 110 includingdielectric layers 111 and a plurality of internal electrodes 121 and 122stacked with each of the dielectric layers 111 interposed therebetween,and external electrodes 131 and 132. In this case, as will be describedlater, corners of cover portions A1 and A2 of the body 110 may be formedas curved surfaces.

The body 110 may have a form in which the plurality of dielectric layers111 are stacked, and may be obtained by stacking and then sintering, forexample, a plurality of green sheets. The plurality of dielectric layers111 may have a form in which they are integrated with one another bysuch a sintering process. A shape and a dimension of the body 110 andthe number of stacked dielectric layer 111 are limited to thoseillustrated in the present embodiment, and the body 110 may have a shapesimilar to a rectangular parallelepiped shape, for example, as in a formillustrated in FIG. 1. The body 110 may include a first surface S1 and asecond surface S2 to which the internal electrodes 121 and 122 areexposed, respectively, a third surface S3 and a fourth surface S4opposing each other in a stacking direction (Z direction) of theplurality of dielectric layers 111, and a fifth surface S5 and a sixthsurface S6 connected to the first to fourth surfaces S1, S2, S3, and S4and opposing each other.

The dielectric layer 111 included in the body 110 may include a ceramicmaterial having a high dielectric constant, for example, a BT-basedceramic material, for example, barium titanate (BaTiO₃)-based ceramicmaterial, but may include another material known in the related art aslong as a sufficient capacitance may be obtained. The dielectric layer111 may further include an additive, an organic solvent, a plasticizer,a binder, a dispersant, and the like, as necessary, together with theceramic material, which is a main component. In this case, the additivesmay include a metal component, and may be added in a metal oxide form ina manufacturing process. An example of such a metal oxide additive mayinclude at least one of MnO₂, Dy₂O₃, BaO, MgO, Al₂O₃, SiO₂, Cr₂O₃, andCaCO₃.

In the present embodiment, as compared in FIGS. 3 and 5, a surfaceroughness of each of the third to sixth surfaces S3 to S6 may be greaterthan a surface roughness of each of the first and second surfaces S1 andS2. The third to sixth surfaces S3 to S6 may be obtained by forming acoating layer on the outer surface in such a manner that ceramic slurryis coated as described later with respect to the manufacturing method ofthe body 110. The inventors of the present disclosure have confirmedthat such a method may be higher than a method of stacking ceramic greensheets, in view of a surface roughness of the body 110. Since the body110 has a high surface roughness, the bonding strength with the externalelectrodes 131 and 132 may be improved, which may lead to enhancement ofmoisture resistance reliability of the body 110 and the like. In thecase of the first and second surfaces S1 and S2, a surface grindingprocess for exposing the internal electrodes 121 and 122 and the likemay be applied, such that the surface roughness may be relatively low.

For example, the surface roughness of each of the third to sixthsurfaces S3 to S6 may satisfy the following relationship of Ra, based onan average calculation method: 0.2<Ra<0.6. In this case, the averagecalculation method (unit: μm) may be one standard for calculating thesurface roughness used in the related art, and may be obtained byaveraging the roughness on the sampled surface with respect to thecenter line.

Further, as another reference of the surface roughness, the surfaceroughness of the third to sixth surfaces S3 to S6 may satisfy thefollowing relationship of Rt, based on a maximum height calculationmethod: 2.0<Rt<5.0. The maximum height calculation method (unit: μm) maybe also one standard for calculating the surface roughness used in therelated art, and may be obtained from the roughness at the farthest fromthe center line, after defining the sample section.

As another reference of the surface roughness, the surface roughness ofthe third to sixth surfaces S3 to S6 may satisfy the followingrelationship of Rz, based on a ten-point average calculation method:2.0<Rz<5.0. The ten-point average calculation method (unit: μm) may bealso one standard for calculating the surface roughness used in therelated art, and may be values obtained by adding the sum (absolutevalue) of the five distances farthest from the center line of the samplesection in an upward direction and the sum (absolute value) of the fivedistances farthest from the center line of the sample section in andownward direction, and dividing the added sum by 5.

Each of the plurality of internal electrodes 121 and 122 may be obtainedby printing and then sintering a paste including a conductive metal at apredetermined thickness on one surface of the ceramic green sheet. Inthis case, the plurality of internal electrodes 121 and 122 may includefirst and second internal electrodes 121 and 122 exposed, respectively,to the first surface S1 and the second surface S2 of the body 110opposing each other, as in a form illustrated in FIG. 3. In this case,the first and second internal electrodes 121 and 122 may be connected todifferent external electrodes 131 and 132, respectively, to havedifferent polarities when the multilayer capacitor is driven, and may beelectrically separated from each other by each of the dielectric layers111 disposed therebetween. As in an illustrated form, the plurality ofinternal electrodes 121 and 122 may have a uniform width. According toanother embodiment, the number of external electrodes 131 and 132 and aconnection manner of the internal electrodes 121 and 122 may be changed.An example of a main material constituting the internal electrodes 121and 122 may include nickel (Ni), copper (Cu), palladium (Pd), silver(Ag), or the like, or alloys thereof.

The external electrodes 131 and 132 may include first and secondexternal electrodes 131 and 132 formed on external surfaces of the body110 and electrically connected, respectively, to the first and secondinternal electrodes 121 and 122. The external electrodes 131 and 132 maybe formed by a method of manufacturing a material including a conductivemetal in a form of a paste and then applying the paste to the body 110,and an example of the conductive metal may include nickel (Ni), copper(Cu), palladium (Pd), gold (Au), or alloys thereof. In addition, theexternal electrodes 131 and 132 may further include plating layers, asnecessary, to mount the multilayer capacitor 100 on a substrate.

In the present embodiment, corners of the body 110 may be formed ascurved surfaces to suppress a chipping defect. In addition, structuralcharacteristics of the body 110 according to the present embodiment maybe expressed unlike those described above. In detail, if a distance froma surface of the body 110 to an internal electrode closest to thesurface of the body 110 among the plurality of internal electrodes 121and 122 refers to a margin, a margin of each of the corners formed asthe curved surfaces in the cover portions A1 and A2 may be greater thanor equal to a margin of the body 110 in a width direction, which will bedescribed below.

In the present embodiment, a size of the margin, a radius of curvatureof the curved surface, a thickness, a distance, and the like, in thebody 110 may be optimized in order to improve performance of themultilayer capacitor. Due to having such a structure, the multilayercapacitor 100 may have a high level of capacitance in spite of beingminiaturized, and furthermore, may have improved moisture resistancereliability. This will hereinafter be described in detail.

The body 110 may be divided into the central portion A3 and the coverportions A1 and A2. In this case, the central portion A3 may correspondto a region forming a capacitance by the plurality of internalelectrodes 121 and 122 disposed therein. The cover portions A1 and A2may be disposed on upper and lower surfaces of the central portion A3,respectively, in the stacking direction (the Z direction in thedrawings) of the plurality of dielectric layers 111. According to anembodiment, the internal electrodes 121 and 122 may be disposed in thecover portions A1 and A2.

As described above, in the cover portions A1 and A2 of the body 110, thecorners may be formed as the curved surfaces, which may serve to reducethe chipping defect of the multilayer capacitor 100, and the like. Indetail, in the cover portions A1 and A2, corners (upper curved surfacecorners in FIG. 2) at which the third surface S3 is connected to thefifth surface S5 and the sixth surface S6, and corners (lower curvedsurface corners in FIG. 2) at which the fourth surface S4 is connectedto the fifth surface S5 and the sixth surface S6 may be formed as curvedsurfaces.

Referring to FIG. 6, optimal conditions of the size of the margin andthe radius of curvature, the thickness, the length, and the like, of thecurved surface in the body 110 will be described. In FIG. 6, a region inwhich the internal electrodes are disposed is defined as an internalelectrode region 120 and is denoted by dotted lines. In this case, a Zdirection refers to a thickness direction of the body 110, a Y directionrefers to a width direction of the body 110, and T and W refer to athickness and a width of the body 110, respectively.

First, a margin of the body 110 may be defined as a distance from thesurface of the body to the internal electrode closest to the surface ofthe body among the plurality of internal electrodes. In detail, a marginof each of the corners formed as the curved surfaces in the coverportions A1 and A2 may be δ. In addition, a margin of each of the fifthsurface S5 and the sixth surface S6 may be Wg, which corresponds to amargin of the body 110 in the width direction. In the presentembodiment, the margin δ of the curved surface corner may be greaterthan or equal to the margin Wg of the body in the width direction. Inthe related art, the internal electrodes were not aligned with eachother, such that it was difficult to form the margin of the body in thewidth direction. In order to solve such a problem, a process ofseparately forming the margin of the body in the width direction wasused. In such a structure, it is difficult to sufficiently secure themargin δ of the curved surface corner of the body 110, and particularlyin a case in which the body 110 is miniaturized and the number ofstacked internal electrodes is increased, moisture resistancereliability may be deteriorated.

In the present embodiment, as described below, the corners of the body110, more specifically, the corners of the cover portions A1 and A2 maybe formed as the curved surfaces by a process of spraying a ceramicpaste, which is more appropriate for forming margin regions in the body110 having a low gradient form. Due to such a form, the margin δ of thecurved surface corner may be sufficiently secured, and may be greaterthan or equal to the margin Wg of the body in the width direction. Inmore detail, 1≤δ/Wg<1.2 in which δ is the margin of the curved surfacecorner and Wg is the margin of the body in the width direction. When themargin δ of the curved surface corner exceeds 1.2 times the margin Wg ofthe body in the width direction, widths of the internal electrodes 121and 122 in the cover portions A1 and A2 may be significantly reduced,such that a capacitance may be reduced.

As the margin δ of the curved surface corner increases, the moistureresistance reliability may be improved even in the miniaturized body110, and the body 110 may include a number of internal electrodes 121and 122 to implement an improved capacitance. This means an increase inthe capacitance, for example, an effective volume, when calculated onthe basis of the same volume of the body 110.

In the present embodiment, the internal electrodes 121 and 122 disposedin the central portion A3 may have a uniform width. The uniform width ofthe internal electrodes 121 and 122 may be achieved by a process ofdicing a ceramic laminate in individual chip units, as described below.In this case, uniformity of the width of the internal electrodes 121 and122 may be determined on the basis of positions of end portions of theinternal electrodes 121 and 122, and a deviation of the positions of theend portions of the internal electrodes 121 and 122 in the widthdirection (the Y direction) may be smaller than or equal to 0.1 μm.

In addition, 0.8≤Tg/Wg≤1.2 in which Tg is a margin of the body 110 inthe thickness direction, for example, a margin of each of the thirdsurface S3 and the fourth surface S4, and Wg is the margin of the bodyin the width direction. As described above, the margin Tg of the body inthe thickness direction and the margin Wg of the body in the widthdirection may be formed by the same process, and may thus have sizessimilar to each other. When dielectric layers 111 corresponding to baselayers for covers are formed on the uppermost and lowermost internalelectrodes 121 and 122, respectively, the margin Tg of the body 110 inthe thickness direction may be slightly greater than the margin Wg ofthe body in the width direction. Also, in this case, Tg/Wg may notexceed 1.2.

In addition, the margin Wg of the body in the width direction maysatisfy the following relationship 0.5 μm≤Wg≤15 μm, and the margin Wg ofthe body in the width direction may be designed to secure the moistureresistance reliability of the body 110 and secure a sufficientcapacitance. Likewise, the margin Tg of the body in the thicknessdirection may also satisfy the following relationship 0.5 μm≤Tg≤15 μm.In addition, the margin Wg of the body in the width direction may be setin consideration of the thickness T of the body 110, and specifically,0.5 μm≤Wg≤T/12. In this case, the thickness T of the body 110 may be,for example, about 200 to 400 μm.

In addition, the radius R of curvature of each of the corners formed asthe curved surfaces in the cover portions A1 and A2 may be designed toendure a weight of the multilayer capacitor 100 and chipping due to aload in a process, and specifically, 10 μm≤R≤60 μm. In addition, theradius R of curvature may be set in consideration of the thickness T ofthe body 110, and specifically, 10 μm≤R≤T/4. As described above, thethickness T of the body 110 may be, for example, about 200 to 400 μm. Inaddition, as in a form illustrated in FIG. 6, in the curved surfacecorners of the cover portions A1 and A2, the radius R of curvature andthe margin δ may be the same as each other. In this case, the curvedsurface corner may correspond to a part of a spherical surface. Theradius R of curvature and the margin δ may also be different from eachother depending on a shape of each of the curved surface corners of thecover portions A1 and A2. For example, each of the curved surfacecorners of the cover portions A1 and A2 may be formed as an asphericalsurface.

In the body 110, when outer regions surrounding the plurality ofinternal electrodes 121 and 122, for example, regions surrounding aninternal electrode region 120 in FIG. 6 are margin regions 112 and 113,a packing factor of the dielectric layer 111 may be lower in the marginregions 112 and 113 than in the other regions. As described below, themargin regions 112 and 113 may be obtained in a manner of manufacturingand then coating a ceramic laminate, and a difference in the packingfactor may be due to a difference in such a manufacturing manner. Inthis case, the packing factor may be understood as a concept that isinversely proportional to a density of pores existing in the dielectriclayer.

FIGS. 7 and 8 are views illustrating shapes of a body and an internalelectrode that may be employed in a multilayer capacitor according toanother embodiment of the present disclosure.

Referring to FIG. 7, a body 110 may be divided into a central portion A3and cover portions A1 and A2. The cover portions A1 and A2 may bedisposed on upper and lower surfaces of the central portion A3,respectively, in a stacking direction (a Z direction in the drawings) ofthe plurality of dielectric layers 111. Internal electrodes 121 and 122may be disposed in the cover portions A1 and A2 and the central portionA3, and a width of an internal electrode disposed in the cover portionsA1 and A2 may be narrower than a width of an internal electrode disposedin the central portion A3. In this case, as illustrated in the drawings,a width of an internal electrode, disposed closer to the surface of thebody among the plurality of internal electrodes 121 and 122 disposed inthe cover portions A1 and A2, is narrower. Widths of the plurality ofinternal electrodes 121 and 122 may be defined as widths in a directionperpendicular to the direction (the X direction) connecting the firstsurface S1 and the second surface S2, and as widths in a directionperpendicular to the stacking direction (the Z direction) of theplurality of dielectric layers 111, i.e., as widths in the Y direction.

As described above, in the cover portions A1 and A2 of the body 110, thecorners may be formed as the curved surfaces, which may serve to reducethe chipping defect of the multilayer capacitor 100. In detail, in thecover portions A1 and A2, corners (upper curved surface corners in FIG.2) at which the third surface S3 is connected to the fifth surface S5and the sixth surface S6, and corners (lower curved surface corners inFIG. 2) at which the fourth surface S4 is connected to the fifth surfaceS5 and the sixth surface S6 may be formed as curved surfaces.

Referring to FIG. 8, optimal conditions of the size of the margin andthe radius of curvature, the thickness, the length, and the like, of thecurved surface in the body 110 will be described. In FIG. 6, a region inwhich the internal electrodes are disposed is defined as an internalelectrode region 120 and is denoted by dotted lines. In this case, a Zdirection refers to a thickness direction of the body 110, a Y directionrefers to a width direction of the body 110, and T and W refer to athickness and a width of the body 110, respectively.

First, a margin of the body 110 may be defined as a distance from thesurface of the body to the internal electrode closest to the surface ofthe body among the plurality of internal electrodes. In detail, a marginof each of the corners formed as the curved surfaces in the coverportions A1 and A2 may be δ. In addition, a margin of each of the fifthsurface S5 and the sixth surface S6 may be Wg, which corresponds to amargin of the body 110 in the width direction. In the presentembodiment, the margin δ of the curved surface corner may be greaterthan or equal to the margin Wg of the body in the width direction. Inthe related art, the internal electrodes were not aligned with eachother, such that it was difficult to form the margin of the body in thewidth direction. In order to solve such a problem, a process ofseparately forming the margin of the body in the width direction wasused. In such a structure, it is difficult to sufficiently secure themargin δ of the curved surface corner of the body 110, and particularlyin a case in which the body 110 is miniaturized and the number ofstacked internal electrodes is increased, moisture resistancereliability may be deteriorated.

In the present embodiment, widths of the internal electrodes 121 and 122disposed on the cover portions A1 and A2 may be adjusted to have a shapecorresponding to the curved surface corner of the body 110 in a whole.Due to such a form, the margin δ of the curved surface corner may besufficiently secured, and may be greater than or equal to the margin Wgof the body in the width direction. In more detail, 1≤δ/Wg≤1.2 in whichδ is the margin of the curved surface corner and Wg is the margin of thebody in the width direction. When the margin δ of the curved surfacecorner exceeds 1.2 times the margin Wg of the body in the widthdirection, widths of the internal electrodes 121 and 122 in the coverportions A1 and A2 may be significantly reduced, such that a capacitancemay be reduced.

As the margin δ of the curved surface corner increases, the moistureresistance reliability may be improved even in the miniaturized body110, and the body 110 may include a number of internal electrodes 121and 122 to implement an improved capacitance. This means an increase inthe capacitance, for example, an effective volume, when calculated onthe basis of the same volume of the body 110.

In the present embodiment, the internal electrodes 121 and 122 disposedin the central portion A3 may have a uniform width. The uniform width ofthe internal electrodes 121 and 122 may be achieved by a process ofdicing a ceramic laminate in individual chip units, as described below.In this case, uniformity of the width of the internal electrodes 121 and122 may be determined on the basis of positions of end portions of theinternal electrodes 121 and 122, and a deviation of the positions of theend portions of the internal electrodes 121 and 122 in the widthdirection (the Y direction) may be smaller than or equal to 0.1 μm.

In addition, 0.8≤Tg/Wg≤1.2 in which Tg is a margin of the body 110 inthe thickness direction, for example, a margin of each of the thirdsurface S3 and the fourth surface S4, and Wg is the margin of the bodyin the width direction. As described above, the margin Tg of the body inthe thickness direction and the margin Wg of the body in the widthdirection may be formed by the same process, and may thus have sizessimilar to each other. When dielectric layers 111 corresponding to baselayers for covers are formed on the uppermost and lowermost internalelectrodes 121 and 122, respectively, the margin Tg of the body in thethickness direction may be slightly greater than the margin Wg of thebody in the width direction. Also, in this case, Tg/Wg may not exceed1.2.

In addition, the margin Wg of the body in the width direction maysatisfy the following relationship 0.5 μm≤Wg≤15 μm, and the margin Wg ofthe body in the width direction may be designed to secure the moistureresistance reliability of the body 110 and secure a sufficientcapacitance. Likewise, the margin Tg of the body in the thicknessdirection may also satisfy the following relationship 0.5 μm≤Tg≤15 μm.In addition, the margin Wg of the body in the width direction may be setin consideration of the thickness T of the body 110, and specifically,0.5 μm≤Wg≤T/12. In this case, the thickness T of the body 110 may be,for example, about 200 to 400 μm.

In addition, the radius R of curvature of each of the corners formed asthe curved surfaces in the cover portions A1 and A2 may be designed toendure a weight of the multilayer capacitor 100 and chipping due to aload in a process, and specifically, 10 μm≤R≤60 μm. In addition, theradius R of curvature may be set in consideration of the thickness T ofthe body 110, and specifically, 10 μm≤R≤T/4. As described above, thethickness T of the body 110 may be, for example, about 200 to 400 μm. Inthis case, a curved surface region of the internal electrode region 120in the cover portions A1 and A2 may have a substantially curved shape,for example, substantially the same curvature as that of the corner ofthe body 110, and the curved surface region of the internal electroderegion 120 may be an imaginary plane obtained by connecting the endportions of the internal electrodes 121 and 122 arranged in the coverportions A1 and A2 in the stacking direction. As illustrated in thedrawings, corners formed by the imaginary plane of the internalelectrode region 120 and the curved surface of the cover portions A1 andA2 may face each other.

Further, as illustrated in FIG. 8, in a case of an imaginary planeobtained by connecting the end portions of the internal electrodes 121and 122 arranged in the cover portions A1 and A2 in the stackingdirection, curvature radius r may be smaller than curvature radius R ofa corner formed as a curved surface in the cover portions A1 and A2. Inthis case, the curvature radii r and R may share a center.

The curvature radius R of the curved corner of the cover portions A1 andA2 may be the same as those calculated by adding the curvature radius rof the imaginary plane to the margin δ of each of the corners formed bythe curved surfaces of the cover portions A1 and A2.

An example of a manufacturing method will be described with reference toFIGS. 9 to 18 to more clearly understand the structure of theabove-described multilayer capacitor.

First, as in a form illustrated in FIG. 9, a ceramic laminate 115 may beprepared by stacking dielectric layers 111 and internal electrodes 121and 122. In this case, since the dielectric layer 111 is in a statebefore being sintered, the dielectric layer 111 may be in a state of aceramic green sheet. The ceramic green sheet may be manufactured bymixing ceramic powders, a binder, a solvent, and the like, with oneanother to prepare slurry, and manufacturing the slurry in a sheet shapehaving a thickness of several micrometers by a doctor blade method.Then, the ceramic green sheet may be sintered to form the dielectriclayer 111.

A conductive paste for an internal electrode may be applied onto theceramic green sheet to form an internal electrode pattern on the ceramicgreen sheet. In this case, the internal electrode pattern may be formedby a screen printing method or a gravure printing method. The conductivepaste for an internal electrode may include a conductive metal and anadditive. The additive may be one or more of a non-metal and a metaloxide. The conductive metal may include nickel. The additive may includebarium titanate or strontium titanate as the metal oxide.

A plurality of ceramic green sheets on which the internal electrodepatterns are formed may be stacked and pressed to implement a ceramiclaminate 115. In this case, the ceramic laminate 115 may include thedielectric layers 111 as base layers for covers disposed at an uppermostportion and a lowermost portion thereof to effectively protect theinternal electrodes 121 and 122. The dielectric layers 111 may not bedisposed at the uppermost portion and the lowermost portion of theceramic laminate 115.

After the ceramic laminate 115 is formed, the ceramic laminate 115 maybe diced in individual chip units, as necessary. In this case, theinternal electrodes 121 and 122 may be exposed in order to be connectedto the external electrodes. The internal electrodes 121 and 122 exposedby a dicing process may have a uniform width. For example, a differencebetween the largest width and the smallest width of the internalelectrodes 121 and 122 may be equal to or less than 0.1 μm.

Then, coating layers 118 (see FIG. 15) may be formed on surfaces of theceramic laminate 115. To this end, an appropriate coating operation maybe performed. In the present embodiment, as in a form illustrated inFIG. 10, a method of spray-coating ceramic slurry 202 using a sprayapparatus 201 may be used. In this case, the ceramic slurry 202 mayfurther include the same component as that of the green sheet forforming the dielectric layer 111 or a component giving fluidity to thegreen sheet, for example, a liquid binder, or the like. FIG. 11illustrates a process of manufacturing the multilayer capacitoraccording to the embodiments of FIGS. 7 and 8, and the coating operationmay be the same as that of FIG. 10. In order to obtain the shapes ofFIGS. 7 and 8, an operation of grinding the corner of the ceramiclaminate 115 to have a curved surface may be further included. In thisoperation, the internal electrodes 121 and 122 arranged in the uppermostportion and the lowermost portion (corresponding to the cover portion ofthe above-described) may be ground together such that the internalelectrodes 121 and 122 are exposed from the ceramic laminate 115. By thegrinding operation, the plurality of internal electrodes 121 and 122,which may be arranged on the cover portion of the body, may be formed ina narrower width than that arranged in the central portion. In thegrinding operation of the corners of the ceramic laminate 115, barrelgrinding or the like may be used. The following description of thecoating operation and subsequent operation(s) may be applied to theoperation for obtaining the structures of FIGS. 7 and 8.

An example of the present coating operation will be described. First, asin forms illustrated in FIGS. 12 and 13, the ceramic laminates 115 maybe disposed in a coating apparatus 301, and air currents (denoted byarrows in FIGS. 12 and 13) may be generated from a lower portion towardan upper portion in the coating apparatus 301. After the ceramiclaminate 115 is floated in this manner, the ceramic slurry 202 may besprayed to the ceramic laminate 115 through a nozzle of the sprayapparatus 201 disposed on the lower portion (see FIG. 12) or the upperportion (see FIG. 13) of the coating apparatus 301. Unlike the formsillustrated therein, the spraying apparatus 201 may also be disposed ona side portion of the coating apparatus 301. The coating layers 118having a uniform thickness may be formed on the surfaces of the ceramiclaminates 115 in such a coating manner. The coating layers 118 areseparately formed after the ceramic laminate 115 is manufactured, suchthat a margin region of the body may be uniformly and thinly formed, anda margin having a sufficient thickness in a corner region of the bodyhaving a poor moisture resistance performance may be obtained.

In addition, as another coating manner, as in a form illustrated in FIG.14, a coating apparatus 302 having a spherical container form may beused. In this case, protrusions 303 may be formed on an inner side ofthe coating apparatus 302. The ceramic laminate 115 may be overturnedand moved while the coating apparatus 302 is rotated. In this process,the ceramic laminate 115 may be uniformly coated.

FIG. 15 is a view illustrating a state in which the coating layers 118are formed on all the surfaces of the ceramic laminate 115, and FIG. 16is a cross-sectional view taken along line III-III′ of FIG. 15. As in aform illustrated therein, when the ceramic laminate 115 is subjected tothe coating operation described above, corners of the coating layers 118may have curved surfaces. Then, the ceramic laminate 115 may be sinteredin a state in which the coating layers 118 are applied. Therefore, theceramic green sheets included in the ceramic laminate 115 and thecoating layers 118 may become an integral body. Further, as describedabove, the body obtained by the coating operation has a higher surfaceroughness than that obtained by the conventional stacking process.

After a sintering process, a portion of the body 110 may be removed toexpose the internal electrodes 121 and 122. In this case, surfaces ofthe body on which the internal electrodes 121 and 122 are exposed maycorrespond to the first surface S1 and the second surface S2 describedwith reference to FIG. 1. Other surfaces of the body may also beexposed, as necessary. As a surface grinding process of removing theportion of the body 110, a grinding process, or the like, may be used.FIG. 17 illustrates the body 110 subjected to the surface grindingprocess after the sintering process and the internal electrodes 121 and121 exposed from the body 110. Then, external electrodes may be formedto be connected to the exposed internal electrodes 121 and 122.

Meanwhile, in the process described above, the dielectric layer 111 maybe formed of the ceramic green sheet, and margin regions may be formedby a coating operation by the spraying of the ceramic slurry. Therefore,there may be a difference in an internal structure of the body after thesintering process. For example, characteristics such as a packing factoror the like may be different between the internal electrode region 120and the margin regions 112 and 113 of the body 110. This will bedescribed with reference to FIG. 18. FIG. 18 is an enlarged plan viewillustrating region A of FIG. 18.

When comparing a packing factor of the dielectric layer 111 between themargin regions and a region (for example, the internal electrode region)other than the margin regions in the body 110, the packing factor may berelatively lower in the margin regions 112 and 113 than in the regionother than the margin regions. In addition, in the margin regions 112and 113, a packing factor may be relatively higher in a region close tothe internal electrodes 121 and 122 than in a region close to an outerportion of the body 110. For example, in the margin regions 112 and 113,the dielectric layers 111 may be at least two layers having differentpacking factors, and a packing factor of the dielectric layer 111 may befurther higher in a layer, adjacent to the plurality of internalelectrodes 121 and 122, of the at least two layers.

These packing factor characteristics of the margin regions 112 and 113may be obtained by the coating operation described above. When theceramic slurry is sprayed, several-fold thin coating layers may beformed on the surfaces of the ceramic laminate 115, and a plurality ofpores may be formed between the coating layers and may remain even afterthe sintering process. As illustrated in FIG. 18, a plurality ofneedle-like pores P may remain in the margin regions 112 and 113 of thebody 110. Since the plurality of needle-like pores P are generated in aprocess of forming the several-fold thin coating layers, a plurality ofrows R1, R2, and R3 formed by the plurality of needle-like pores P mayhave a form in which they are aligned in a shape corresponding to anappearance of the body 110. Pore densities of the plurality of rows R1,R2, and R3 by the plurality of needle-like pores P may be different fromone another, and as a region becomes closer to the surface of the body,the region may be later coated, and a pore density of the region maythus be relatively lower.

As set forth above, the multilayer capacitor according to the embodimentin the present disclosure may be advantageous in terms ofminiaturization, may have a high capacitance, and may have excellentmoisture resistance characteristics to have a high reliability.

According to an embodiment of the present disclosure, the multilayercapacitor may be advantageous in terms of miniaturization, may have ahigh capacitance, and may have excellent moisture resistancecharacteristics to have a high reliability. In addition, the bondingstrength between the body and the external electrode may increase toimprove the moisture resistance reliability.

While embodiments have been shown and described above, it will beapparent to those skilled in the art that modifications and variationscould be made without departing from the scope of the present disclosureas defined by the appended claims.

What is claimed is:
 1. A multilayer capacitor comprising: a bodyincluding a stacked structure having a plurality of dielectric layers,and a plurality of internal electrodes stacked with the plurality ofdielectric layers interposed therebetween; and external electrodesdisposed on external surfaces of the body and electrically connected tothe plurality of internal electrodes, wherein the body has a centralportion, and cover portions disposed above and below the central portionin a stacking direction of the plurality of dielectric layers, the bodyhas a first surface and a second surface from which the plurality ofinternal electrodes are exposed and which oppose each other, a thirdsurface and a fourth surface which oppose each other in the stackingdirection of the plurality of dielectric layers, and a fifth surface anda sixth surface which are connected to the first to fourth surfaces andoppose each other, and a surface roughness of each of the third to sixthsurfaces of the body is greater than a surface roughness of each of thefirst and second surfaces of the body.
 2. The multilayer capacitoraccording to claim 1, wherein the surface roughness, Ra, of each of thethird to sixth surfaces satisfies the following relationship, based onan average calculation method:0.2 μm<Ra<0.6 μm.
 3. The multilayer capacitor according to claim 1,wherein the surface roughness, Rt, of each of the third to sixthsurfaces satisfies the following relationship, based on a maximum heightcalculation method:2.0 μm<Rt<5.0 μm.
 4. The multilayer capacitor according to claim 1,wherein the surface roughness, Rz, of each of the third to sixthsurfaces satisfies the following relationship, based on a ten-pointaverage calculation method:2.0 μm<Rz<5.0 μm.
 5. The multilayer capacitor according to claim 1,wherein corners of the cover portions in the body have curved surfaces.6. The multilayer capacitor according to claim 5, wherein a radius R ofcurvature of each of the curved corners and a thickness T of the bodysatisfy the following relationship:10 μm≤R≤T/4.
 7. The multilayer capacitor according to claim 5, wherein,a margin Wg of each of the fifth and sixth surfaces from each of thefifth and sixth surfaces to an internal electrode closest to the surfaceof the body among the plurality of internal electrodes, and a margin Tgof each of the third and fourth surfaces from each of the third andfourth surfaces to an internal electrode closest to the surface of thebody among the plurality of internal electrodes, satisfy the followingrelationship:0.8≤Tg/Wg≤1.2.
 8. The multilayer capacitor according to claim 5, whereincorners at which the third surface is connected to the fifth and sixthsurfaces, and corners at which the fourth surface is connected to thefifth and sixth surfaces, have curved surfaces in the cover portions. 9.The multilayer capacitor according to claim 8, wherein a margin δ ofeach of the corners having curved surfaces in the cover portions isgreater than or equal to a margin Wg of each of the fifth and sixthsurfaces.
 10. The multilayer capacitor according to claim 9, wherein themargins (δ and Wg) satisfy the following relationship:1≤δ/Wg≤1.2.
 11. The multilayer capacitor according to claim 1, whereinthe plurality of internal electrodes have a uniform width.
 12. Themultilayer capacitor according to claim 1, wherein, in the plurality ofinternal electrodes, a width of an internal electrode disposed in thecover portion is narrower than a width of an internal electrode disposedin the central portion.
 13. The multilayer capacitor according to claim12, wherein, a width of the internal electrode, disposed closer to thesurface of the body among the plurality of internal electrodes disposedin the cover portion, is narrower.
 14. The multilayer capacitoraccording to claim 12, wherein widths of the plurality of internalelectrodes are widths in a direction perpendicular to a directionconnecting the first surface and the second surface, and widths in adirection perpendicular to the stacking direction of the plurality ofdielectric layers.
 15. A multilayer capacitor comprising: a bodyincluding: a stacked structure having dielectric layers, and first andsecond internal electrodes stacked with the dielectric layers interposedtherebetween and respectively exposed from end surfaces of the body, anda margin covering the stacked structure except the end surfaces; andfirst and second external electrodes disposed on the end surfaces of thebody and electrically connected to the first and second internalelectrodes, respectively, wherein a surface roughness of the margin isgreater than a surface roughness of each of the end surfaces, andopposing ends of each of the first and second internal electrodes, in awidth direction of the body, are in contact with the margin.
 16. Themultilayer capacitor according to claim 15, wherein the first and secondinternal electrodes include, central internal electrodes, upper internalelectrodes, and lower internal electrodes, the central internalelectrodes are disposed between the upper internal electrodes and thelower internal electrodes, a difference between a largest width and asmallest width of the central internal electrodes is less than 0.1 μm, awidth of the upper internal electrodes decreases in a direction from thecentral internal electrodes to the upper internal electrodes, and awidth of the lower internal electrodes decreases in a direction from thecentral internal electrodes to the lower internal electrodes.
 17. Themultilayer capacitor according to claim 15, wherein a difference betweena largest width and a smallest width of the internal electrodes is lessthan 0.1 μm, and a distance, in a stacking direction of the dielectriclayers, from an uppermost inner electrode of the first and secondinternal electrodes to an exterior upper surface of the margin, or adistance, in the stacking direction of the dielectric layers, from alowermost inner electrode of the first and second internal electrodes toan exterior lower surface of the margin, is greater than a distance, inthe width direction of the body, from each of the first and secondinternal electrodes to an exterior side surface of the margin.
 18. Themultilayer capacitor according to claim 15, wherein one of the followingconditions is satisfied: 0.2 μm<Ra<0.6 μm, in which Ra is the surfaceroughness of margin based on an average calculation method, 2.0μm<Rt<5.0 μm, in which Rt is the surface roughness of margin based on amaximum height calculation method, and 2.0 μm<Rz<5.0 μm, in which Rz isthe surface roughness of margin based on a ten-point average calculationmethod.
 19. The multilayer capacitor according to claim 15, wherein themargin includes a plurality of layers each having pores.
 20. Themultilayer capacitor according to claim 15, wherein a thickness of acurved portion of the margin at a corner of the body is equal to greaterthan a thickness of a flat portion of the margin disposed on a sidesurface of the body in the width direction.